Hydraulic transmission



w. R; TUCKER HYDRAULIC TRANSMISSION Sept; 4, 1945.

Filed May 31, 1941 4 Sheets-Sheet 3 FIE=4- Sept. 4, 1945 w, R, TUCKER 2,384,218 I HYDRAULIC TRANSMISSION Filed May 31, 1941 f4 Sheets-Sheet 4 Patented Sept. 4, 1945 UNITED STATES the pump and motor is confined within the pump 1 casing. 1

Another object of the invention is to provide a hydraulic t wherein the pumpand motor are identical units supported from a com- 7 mon dividing wall separating the pum from the motor.

Another object of the invention is to provide a vane pump which can be used for either the pump or motor of a hydraulic on.

V Another object of the invention is to provide a vane pump for a hydraulic on which can be used aseither the pump or motor having means for positive actuation'of the vanes.

It is another object. of the invention to provide a hydraulic on in accordancewith hydraulic transmission using vane pumps as the the foregoing object wherein the positive. actuating means consistsor a floating central plug in engagement with the inner ends of the vanes. Another object of the invention is to provide a hydraulic on in accordance with the previous object wherein the plug is tapered md means are provided for moving-the pump or motor with respect to the actuating plug thereof foradiustingthepositionofthevaneswithin the pump or motor. Another object of the invention is to provide a hydraulic on wherein vane pumps asthe pump and motor having means for adjusting the posiflon of the vaneswithin the pump by movement of the entire pump or motor 1' Another object of the invention 1510 provide ahydraulic t'uslng vane pumlilas the pumpandmotor thereof having means for yd l s r retaining the vanes in t with their respective operating cylinders.

'Anothcr-obiectoftheinventionistoprovidca hydraulic pumps B the pumpandmotorthereofwhereintherotorsofthe pump and a common shaft. i

*It'is another obiectdtheinventiontoprovide a hydraulic I pmnpimitsiorthepmhpandmotor whgein therotorsofthcpmhnandmotoraresupportedbya apmnpinaeeordanecwiththe obiect PATENT A OFFICE V 2,384.11, v A A I HYDRAULIC TRANSMISSION Warren E. Tucker, Oakwood, Ohio, aasignor to' The Hydraulic Development Corporation, Inc. Wilmington, Del., a corporation of Application May :1 1941, Serial No. 390,032

1 Claims. (cl. 60-53) 'vane pump units as the pump andmotor of a 5 "hydraulic positioned adjacent each other andbearinged upon a common shaft to proator.

Another object of the invention is to provide with respect to' the mechanical actuator to control the clearance between the vanes and the cyl wherein valve means are provided in-thc mission'ior' mouthing positive pressure under stub shalt carriedby a common dividing than be- I tween the pump and motor units.

Another object of the invention is to provide vide a compact unitary on.

A further object of the invention is to provide a hydraulictransmission using vane pumps for the pump and motor thereof wherein the vanes are retained in engagement'with their respective cylinder walls by means of a mechanical actua on in accordance with the foregoing object wherein the-pump assembly is adiustableinder walls of the pump and motor units.

Another object of invention is to provide a hydraulic wherein the mechanical actuator-for the vane pump is adjustable from the exterior of the pump. 7

Another object of the invention is to provide a 'pump and motor thereof wherein the motor pump is provided with a mechanical vane actuator while the power-pump is provided with hydraulic means for actuating the vanes and retaining thasame. in engagement with the pump cylinder wall.

Another object of the invention is to provide at wherein the vane pumps thereof acting as pump and motor areprovided with hypositive hydrauliopreesureto'thevanes ofthe motor to insure engllunent cylindel'wal'llx obiectoltheinventionistoprovidea in accordance with the foregoing hetwcenthemmpandmotorofthetransthe vanesol the motor beio'repermittin'g iiow V Anotherdijectoltheinventionistoprovide of a hydraulic transmission of this invention using vane pumps with mechanically actuated van'e devices.

Figure 2 is a transverse cross-sectional view taken substantially along line 2-2 of Figure 1.

a Figure3 is a longitudinal cross-sectional view of'the motor unit similar to the motorunit of Figure 1 but showing a modified apparatus for adjusting the mechanical actuator for the vanes of the vane pump acting as either motor or pump I of the transmission.

Figure 4 is a longitudinal cross-sectional view of a modified pump arrangement wherein the mechanical actuator of .the pump of Figure 3 is inthe motor'of the transmission and hydraulically actuated vanes-are used in the pump of the transmission. j Figure 5. is a longitudinal cross-sectional view of another modified form of the invention showing a working chamber ll within which a vane type pump unit 12 is positioned. A second chamber I3 is provided in the lower portion of th casing l0 and is arranged to receive the liquid used for circulation between the pump and the motor unit of the hydraulic transmission. a

The pump unit l2 consists of a cylinder l4 which is substantially rectangular as to its excommunicates with'the passage a for the motor I unit I211. The passage. Ila. of the motor unit l2a is the inlet passage for the same, while thepassage Hill is the outlet passage communicating with the return passage I80, to the chamberl3a. The casings I0 and Illa are positioned-adjacent opposite sides of a dividing wall 2| and-are secured together and to the wall 2| by means of suitable bolts 22. The dividing wall 2| is provided with a passage '23 which permits flow'communication between the chambers l3 and I whereby the bottom portion of the housings I0 and I 011 provides a storage chamber for circulating'liquid.

The pump unit l2 includes a rotor 24 having a cylindrical portion 25 positioned within the cylindrical bore I5 01 the cylinder l4 and arranged for rotation'therein. The cylindrical portion 25 has a plurality of slots 26 positioned radially therein within each of which a-vane 21 iscarried. The body of the rotor 24 has a flanged portion 28 which engages the planar surface 29 provided on the cylinder l4 to close one side of the cylindrical chamber I 5. A plate member is positioned adjacent the planar surface 3| pro-- vided on the opposite side of the cylinder l4 and or thelpump illustrated-in Figures 1 and 2 of the drawings.

Inf th isinvention the hydraulic transmission,

shown in Figures 1 and 2, consists of-identical which are separated by a wall member and upon which they are carried for providing a compact Iunitarrangement of pump and motor {or a The casing of the t ansmission'is suitably cored in the lower porti on tfmere'of for-'"receiving liquid which is circulated bii thepump to the motor. With the actuating'li'quid' carried within the pump casing the transmission becomes a complete unit structure v 'ch be. readily connected between any source rp w r nd a. driven apparatus. sm h hswrzma pump units of the transare oi id ritical construction in Figures 1 t l lbefn'ecessary to describe only one of the. units. The pump unit will be particularly s ince rit has a control element assoe jcon structio jThetelements of the motor :2 unit comparablewithithe' elements of the pump unit yville-be designated with the same numeral as e pump unit but with the sum The pump unit consists of a casing l0 having is secured to. the cylindrical portion 26 of the rotor 24 by means or the bolts 32.

To retain the vanes 21in engagement with the cylindrical bore 15 of the cylinder I 4 a mechanical actuator is positioned within the cylindrical bore 33 provided in the rotor 24. The actuator consists of a cylindrical plug 34 which is slightly conical in shape. The vanes 21 have their inner edges tapered to match the taper of the mechanical actuator 34. One end 01' the mechanical actuator 34 engages 'a stub shaft 35 secured within the dividing wall 2|. The opposite end of the mechanical actuator is engaged by a piston member 38 which is pressed against the end of the actuator by means of the sp ng 31. The piston 36 and spring 3'! are carried within a cylindrical bore 38 provided in the rotor 24.

The rotor 24 has a drive shaft 39 as an integral part thereof which extends through the casing l0 and is adapted to be connected to a suitable source of power, such as an electric motor. The shaft 39 is carried upon the tapered roller hearing 40 one race 4| of which is positioned upon the shaft 39 while the other race 42 is carried within the cylindrical bore 43 provided in the casing Ill. The tapered roller bearing 40 thus provides bearing means for one end 01' the rotor 24. The opposite end of the rotor 24 is bearinged upon the stub shaft 35 through means 01' the needle bearings 44 suitably positioned within the end plate 30.

The shaft 88 extends through asealing and adlusting mechanism carried within the end wall the plug 4! in the threaded opening 41 moves the pump unit Il with respect to the mechanical actuator 34 to cause the vanes 21 to ride on a higher portion of the taper of the mechanical actuator 34 and thereby adjust the clearance between the outer ends of the vanes 21 and the cylinder wall I5. Since the mechanical actuator 34 is in engagement with the stationary stub shaft I! it is thus possible to move the entire pumping unit Il with respect to the mechanical actuator 34 to obtain the required adjustment for 1 operating clearance between the vanes ll and the cylinder wall II. II, when making the adjustment, the pumping unit Il should be forced inwardly too far and thus cause binding between the vanes ll and the cylinder wall'll the plug 45 can be slightly retracted to relieve the-binding condition. Under this condition the spring 31 will retain the mechanical actuator 34 against the stub shaft 35 to permit the vanes 21 to slide'with respect to actuator 34 and thus relieve the binding condition.

The adjusting plug is surrounded with a packing gland 4. which is retained in position by means of a packing nut 49. The shaft 39 extends through the adjusting plug 45. A packing gland 5. is provided between the shaft 39 and the plug 45 which is retained in compressed condition by,

means or thepacking'nutil. The cylinder I4 is slidably retained between the parallel surface 52 and 53 provided in the.

casing II, see Figure 2, to permit the eccentricity of the cylinder to be varied with respect to the rotor whereby the capacity of the'pump I2 is controlled. The cylinder I4 can be shifted manually or by suitable automatic means to obtain the desired speed output from the hydraulic transmission. The control members may consist of a spring I4 adapted to be connected to a plung- 1 er II which urges the cylinder toward eccentric or full stroke position. A plunger 58 is positioned within a bore II for opposing the action or the spring I4 and the plunger 55. The plunger 58 can be either manually operated or suitable automatic mechanism can be connected thereto for shifting the cylinder I4 against the action of the plunger II.

, vane pump Il withdraws liquid from the reservoir of liquid stored in the chamber II through the es It and I6 and discharges the same into the passages I1 and ll. The liquid is then conducted from the passage ll into the passage lla and admittedinto the motor pump Ila through the passage Ma. The liquid expends its force upon the vanes within the pump Ila and dlscharges'through the passage "a. By varying the stroke of the pump Il through reciprocation of the cylinder I4 with respect to the rotor -l4 the volume of fluid delivered to the motor Ila is varied and thus the speed 0! the motor is controlled. -The motor Ila can also be provided with a stroke control mechanism whereby additional control over the speed or operation of the motor Ila can be obtained.

Since the pump and the motor are of identical construction it can be seen that a single unit structure can be produced and two units oi. structure can be combined to provide a relatively compact transmission. The placement or the rotors In Figure 3 there is shown a modification of Ila.

ner race ll of which is carried upon the reduced diameter portion II and the outer race 14 is car-- ried within a cylindrical bore I5 provided in'the tained in position within the bore 15 by means the pump Il a the drive shaft for the pump ll. 1

It is to be understood however that the shaft 89a of the motor Ila is not a drive shaft but is a power transmitting shaft which is connected 'to the apparatus adapted to be driven by means of the hydraulic transmission.

a motor ,unit wherein the adjusting mechanism for the mechanical actuator moves the actuator with respect to the pumpingmechanism rather than moving the pump or motor with respect to the mechanical actuator as previously described with regard to Figure 1. In this modification the elements which are similar to the elements of.

Figure-I will be referred to with the same numerals as used in Figure l, the modified structure being additionally described.

In this form of the apparatus the casing Ifla is provided with a working chamber I la in which the motor unit Ila is positioned. Th motor unit consists of the cylinder I4a having an inlet passage IIa and an outlet passage Ilia. The cylinder is reciprocably mounted between the parallel sur- 'faces 52a and 53a provided upon opposite walls of the working chamber Ila. The inlet passage IIa connects with the passage 20a which is in communication with the discharge passage from a similar pump unit associated with the motor unit The discharge passage Ila conducts fluid from the motor unit Ila into the fluid reservoir Ila. 1

Thecylinder I4a is provided. with a rotor which has a cylindrical portion BI positioned within the bore lid of the cylinder Ma. The flanged portion 62 is integral with the portion GI and engages the planar surface 3Ia oi the cylinder I4a for closing one side thereof. The rotor 80 includes a reduced diameter portion 63 which carries a tapered roller bearing 64 one race 65 of which is positioned u-pon the-reduced diameter portion 63 and the other race 66 is car-, ried within'a. recess 61 provided in the dividing plate 88. motor unit Ila from a cooperating pump unit positioned upon the opposite side of the plate '68.

A clos'ure plate 69 engages the planar surface 29a of the cylinder I 4a for closing the cylinder and is secured to the-cylindrical portion CI of the rotor 80 by means of the bolts 10. The closure plate has a reduced diameter portion I which carries a tapered roller bearing ll the incasing Illa. The tapered roller bearing 12 is reof an end closure plate I8. A The vanes l'la carried within radial slots provided in the cylindrical portion ll of the rotor 80 have their outer ends in engagement with the cylinder wall Ila and their inner ends in engagement with a mechanical actuator 34!). The actuator 34b is similar to that described with regard to the actuator 34 of Figure l and performs the same function of retaining the outer ends of the vanes 21a in engagement with the cylinder wall I a. The mechanical actuator 34b has one end thereof in engagement with an adjusting plate 11. The opposite end oi-the mechanical actuathe overall The dividing plate 68 separates the tor is engaged by a piston I8 pressed against the actuator by means of a spring I8 for retaining the opposite end of the actuator 84b in en-' I 88 ofthe rotor 88.

The adjusting plate I1 is positioned within a recess 8I provided within the closure plate 88 which recess cooperates with a recess 82 in the rotor 88 wherein the mechanical actuator 84 can operate.

The adjusting mechanism for the mechanical actuator 84b consists of a plurality of pins 88 extending through bores 84 provided in the reduced diameter portion II of the end closure plate 88. The power take all shaft 88 of the motor I2a is of smaller diameter than the portion II of the end plate 88 whereby a shoulder 88 is provided. The pins 88 extend through the shoulder 88 and engage the inner race 88 of the ball bearing 81. The outer race 88 of the ball bearing 81 is engaged by an adjusting plug 88 which is in threaded engagement with a suitable threaded opening 8I in the end closure plate 18. A packing gland 82 is provided between the adlusting pl 88 and the closure plate 18 while a packing gland 88 is provided between the adjusting plug 88 and the power take off shaft 85.

When the adjusting plug 88 is rotated the pins 88 will be moved inwardly or outwardly with respect to the mechanical actuator 84b whereby the tapered wall of the mechanical actuator cooperating with the tapered inner ends of the vanes 21 will adjust the clearance between the outer ends of the vanes 21 and the cylinder wall lid. The spring I8 will cause the actuator 84b to follow the movement of the adjusting plate 11.

While the description of Figure 3 has been made with reference to the motor unit of a hydraulic transmission it is to be understood that the pump unit can be made identicalwith the motor unit and positioned upon the opposite side of the dividing plate 88. Either or both the pumping unit and the motor unit can have their cylinders adjustable to vary the eccentricity between the cylinder and the rotor for controlling the speed output of the transmission. Such control features have heretofore been referred to with regard to Figure 1 and it is therefore not believed necessary to specifically set forth the contrbls with regard to Figure 3 since'the same type of control mechanism will operate the cylinder of Figure 3 in the same manner asheretofore described with regard to the cylinder of Figure 1. v In Figure 4 there is shown another modified arrangement of a hydraulic transmission using vans pumps as the pumping unit as well as the motor unit. The modifications heretofore described have provided a mechanical actuating de'rdee for maintaining the vanes of the vane pump in engagement with the cylinder wall. When such a mechanical device is used there is no problem of collapsing of the vane of the pump. However. a, hydraulic pressure fluid can be used to maintain the vanes in engagement with the cylinder walls to. replace the mechanical actuator heretofore described. Figure 4 discloses a hydraulic transmission wherein the motor unit is provided with a mechanical actuator for maintaining the vanes in engagement with the cylinder walls while the pumping unit is provided with hydraulic means for performing this funcof Figure 3 is that the reduced diameter portion 88 of the rotor 88 of the motor unit In has an extended portion 88a which protrudes through the dividing plate 88 into the pumping chamber and upon which the rotor of the pumping unit is bearinged. v

The pumping unit 88 of the hydraulic transmission disclosed in Figure 4 consists of a casing I8c having an internal working chamber IIc within which the pumping mechanism is positioned. The casing Me is provided with a fluid reservoir chamber I8c in the lower portion thereof. v

The pumping unit 88 consists of a rotor 88 having an integral drive shaft 81. Closure plates 88 and 88 are provided on opposite faces of the rotor 88 for engaging the planar surfaces I88 and IM of the cylinder I82. The cylinder I82 has a bore I88 within which the rotor 88 is positioned. The rotor 88 carries a plurality of vanes I84 positioned radially within suitable slots provided in the rotor 88 for cooperating with the rotor and the cylinder to produce a vane type pump unit. The rotor elements 88, 88 and 88 are secured in their proper relation bymeans of the bolts I88. I

The rotor 88 is provided with an internal bore I88 which carries a plurality of needle bearings I81 for supporting the rotor 88 upon the extending portion 88a of the motor unit I2c. The drive shaft 81 of the pumping unit 85 carries a tapered roller bearing I88, the inner race I88 of which is carried upon the drive shaft 81 and the outer race 8 being carried within a bore I II provided in the casing IIlc. The tapered bearing I88 is positioned within the; bore III by means of the plug II2 threaded'intb the casing I and sealed by means of the packing glands II! and H4.

The cylinder I,82 is provided with an inlet passage II8 and with an outlet passage H8. The inlet passage II8 is in communication with a passage III which communicates with the fluid within the reservoir I80. The outlet passage II 8 communicates with a passage II8 provided in the casing I8c which is in alignment with a passage III provided in the dividing plate 88 whereby liquid from the pumping unit 88 is conducted to the inlet passage 28:: of the motor unit I2c.

The vanes I84 are shorter than the slots I28 within which. they reciprocate in the cylinder I82. A. space I2I is therefore provided between the lower edge of the vane I84 and the bottom of the slot I28. with the passage I2: provided in the closure plate 88, and which passage is in turn in communication with a passage I28 provided in the wall of the cylinder I82, The passage I22 communicates with an annular groove I24 provided ad- Jacent the space I for distributing fluid conducted to the groove I24 by means of the passages I28 and I22from the discharge passage III of the cylinder I82. The passages I28 and I2: thus permit fluid at discharge pressure to be conducted to the under side of each of the vanes I84 and retain the vanes in engagement with'the cylinder wall I88. I

when the hydraulic ton is not in operation there is substantially no pressure in the discharge passage '8 so that at this time the vanes I84 will be collapsed. However, as soon as the pump unit 88 begins rotation centrifugal force will cause the vanes I84 to move outwardly This space I2I is in communication deliver fluid to the motor. motor is standing idle the vanes will still be in a collapsed condition so that fluid delivered to the into engagement with the cylinder wall I" to establish pumping chambers and thereby produce pressure in the discharge passage II5. Since the will be immediately built up in the passage between the pumping unit 95 and the motor unit I2c thereby substantially immediately applying pressure to the under side of the vanes I04 of the pumping unit 35.

The arrangement of Figure 4thus provides a hydraulic transmission using both hydraulic and mechanical means for actuating the vanes of the vane pumps of the transmission.

In Figure 5 there is disclosed a hydraulic transmission using vane pumps as the pumping device and the motor wherein the vanes of the pumping and motor mechanisms are maintained in engagement with their respective cylinder walls by means of hydraulic pressure. When a pumping mechanism of this type is not operating there is substantially no pressure existing within the mechanism to retain the vanes of the pump and the motor in position in engagement with the cylinder walls whereby the vanes can collapse. When the pump of the transmission starts rotation thevanes of the pump will be moved outwardly by centrifugal force into engagement with the cylinder wall of the pump to However, since the motor can pass through the same without causing rotation thereof. Since the fluid is free to pass through the motor there will be no pressure built up.either in the discharge side of the pump or on the inlet side of the motor. The lack of fluid pressure on the discharge side of the pump leaves the vanes oi the motor without means for moving the same into engagement with the cylinder wall of the motor. Under these conditions the motor might never start. The apparatus of Figure 5 discloses means for insuring development of pressure in the discharge side of the pumping mechanism for transmissionto the under side of the vanes of the motor before the fluid is directed through the motor for rotating the same. Once pressure has 'built'up in the discharge side of the pumping mechanism and has been transmitted to the vanes of the motor, the vanes will remain in their extended position and the fluid can then circulate .through the motor for operating the same. f r

In this modification the casing I0d encloses. a pumping mechanism I25 which is like the pumping mechanism 95 disclosed in Figure 4 wherein the hydraulic pressure from the discharge side of the pumping mechanism I25 is conducted to the under side of the anes for applying pressure thereto. A similar mechanism I30 is enclosed within the casing I 0d,

- closed in Figure 4.

be used.

The rotors 96d of the pump and motor I25 and I30 are bearinged upon a stub shaft I36 secured within the dividing wall I3I. The rotors 35d are carried upon the stub shaft I35 by the needle bearings I05d in the same manner as the rotor 350 is carried upon the stub shaft 53a, as dis- The only difference between the structure of Figure '4 and that of Figure 5 "is that the stub shaft I35 is secured to the wall I3I and thus is able to carry both rotors-of the pump I and the motor I30.

The end closure plate 99d is provided with a passage I31 which communicates with an annular groove I38 in the outer face of the closure .plate 90d. The groove I38 communicates with a plurality of passages I39 extending through the dividing wall I 3I into the motor chamber. The end closure plate 33d'of the motor I is provided with a plurality of passages I40 which communicates with annular grooves I and I42 positioned in opposite faces of the end closure plate Md. The passages I39 in the dividing wall I3I communicate with the annular groove I while the annular groove I42 communicates with'the space I2Id provided heneath the lower edge-of the vane I04d of the motor I30. The hydraulic interconnection between the-pump I25and the motor I30 just de- I scribed is the only structural difference between the units and the unit described with regard I to Figure 4.

which mechanism is the motor of the hydraulic transmission. The pumping mechanisms I25 and I30 areseparated by a dividing wall .I3I which has a rotatable .valve I32 positioned therein. The valve I32 is provided with a pastural details to the pumping mechanism '35 described with regard to Figure 4 a detailed description of the mechanism is not believed essential and the same numerals will therefore be usedon, the mechanisms of Figure 5 to identify However, in order to insure positive pressure to the space I 2Id vof the motor I30 it is necessary that pressure shall be built up in the discharge passage I34 from the pump I25 before fluid is permitted to flow through the inlet passage I35 to the pump I30. The valve I32 performs the function of shutting oif the connection between the passages I34 and I35 when the pressure in the passage I34 is below a predetermined level.

The control apparatus for the valveI32 consists of a piston I43 slidable within a cylinder I44 formed integral with the casings I0d and I0d' one-half the cylinder vbeingcarried by the casing I0d, while the other half is carried by the casing I'0d'. The piston I43 is'provided with a gear rack I45 extending longitudinally thereof,- and which is in engagement with a gear or gear segment I46 carried by the valve I32- A spring I41 is compressed between the piston I43 and an adjusting screwi43, the adiusting screw being carried by the wall. of the cylinder I44. The spring I41 urges the piston in a leftward direction as viewed in Figure 5 to locate the valve I32 in a. position to close the connection between the passages I34 and I35. A passage I49'connects a, recess I50 in the end of the cylinder I44 with the discharge passage I34 from'the pump I25 so that the pressure in the discharge passage I34 is conducted to the left end of the piston I43.

When the transmission is idle the position of the valve I32 and the piston I43 is as disclosed in Figure 5. When the pump unit I25 begins rotation fluid will be delivered into the chamber I34 since the vanes will be thrown outwardly centrifugally by rotation of the rotor 00d, thus delivering fluid under pressure into the chamber I34. When the pressure within the chamelements of like characterand the sufllx d'f will pumping unit or the motor unit of the hydraulic transmission of any of the modifications disclosed have their ecoentricities variable in order to vary the output speed of the transmission.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A hydraulic transmission consisting of a pair of substantially identical unit structures each of which consists of a main housing unit having an open end, a casing for a vane type sure-will have been transmitted to beneath the vanes Ild of the motor I30 and thus insuring the engagement of their outer ends with the cylinder wall I03d oi the motor I30. Since the vanes are in their proper position in engagement with the cylinder wall delivery of fluid from the pumping unit I 20 to the motor unit I30 can then be established.

In Figure 6 there is represented in diagrammatic form the use of a pilot pump for supplying pressure to the passage I30 within the dividing wall Ill of the apparatus of Figure 5. The pilot pump I" may consist of a conventional gear pump for withdrawing liquid from the fluid reservoir lid and delivering the same through the conduit I00 into a suitable port within the dividing wall I 0| ofthe apparatus of Figure 5, for conducting the fluid to thepassage I30. Since the passage I30 communicates with the annular grooves I30 and Ill liquid delivered by the pilot pump will be carried through the passages I31 power unit disposed within said housing and integral therewith, a reservoir chamber within said housing formed between the walls of said housing and said casing and having an open end wall, a vane type power unit mounted within said casing, a power shaft for said power unit extending through a common wall for said casing and said housing and journalled therein, a partition wall plate forming anend closure wall for both of said housings to separate the same into independent power units, said unit structures being mounted "upon opposite sides of said partition wall with said chamber openings adjacent opposite faces of said partition wall, and passages through said partition wall for establishing fluid passage beand I40 to beneath the vanes I0ld of the pump a which there is positioned a by-pass valve I00 for regulating the pressure developed within the con I duit I00 before excess fluid is by-passed to the reservoir I3d. This arrangement permits the pilot pump to produce a substantially constant pressure within the conduit m, and thus a substantially constant pressure below the vanes Ilild of both the pump unit I20 andthe motor unit I30.

Since the pressure supplied by the pilot pump I0! is relatively constant this pressure can be used as a safety control feature as to the maximum pressure developed within the transmission by means of the pump unit I20. The pressure within the discharge chamber I30, acting upon the outer ends of the vanes Illd, always tends to collapse thev vanes against the pressure existing within the space I2Id provided below the tween said power units and between the reservoir chambers in said housings.

2. A hydraulic transmission comprising a pair of substantially identical unit structures each of which consists of a main housing unit having an open end, a casing for a vane type p wer unit disposed within said housing and integral therewith, a reservoir chamber withinsaid housing formed between the walls of said housing and said casing and having an open end wall, a vane type power unit mounted within said casing, a power shaft for said power unit extending through a common wall for said casing and said housing and journalled therein, a partition wall 1 plate forming an end closure wall for both of said housings to separate the same into independent power units, a flow passage in said-casvanes. The pressure delivered by the pilot pump ing connecting said reservoir to said vane type power unit, a second flow passage in said casing "from said vane type power unit to the exterior of said casing and terminating in the same plane as said open end wall, said unit structures being mounted upon opposite faces of said partition with tsald second passages and said chamber openings adjacent opposite faces. of said part1- tion, and passages through said partition interconnecting the reservoir chambers in said housings and said second flow passages, whereby fluid an open end, a casing for a vane type power unit disposed within said housing and integral therewith, a reservoir chamber within said housing formed between the walls of said housing and said casing and having an open end wall,- a vane type power unit mounted within said casing inclosure wall for both or said housings to separate the same into independent power units, a

' bearing shaft extending through said wall plate and upon which the rotors! the power unit is journalled, a flow passage in said casing con- "It is of course to be understood that either he n c s s reservoir to said e pe p e unit, a second flow passage in said casing from said vane type power unit to the exterior of said casing and terminating in the same plane as said open end wall, said unit structures being mounted upon opposite faces of said partition with said second passages and said chamber openings adjaoent opposite faces of said partition, and passages through said partition interconnecting the. reservoir chambersin said housings and said second flow passages, whereby fluid circuit flow is established for the hydraulic transmission.

'4. A hydraulic transmission having a pair of vane pumps operating as the power unit and the motor unit thereof, means for conducting fluid. pressure from the discharge side of the power unit to the under side of the vanes of both of said units for maintaining the outer ends of the vanes in engagement with their respective cylinder walls, and means for establishing positive pressure in the discharge side of said power unit to position the outer ends of the vanes in engagement with their respective cylinder walls before fluid is conducted to the motor unit for actuation thereof.

5. A hydraulic transmission having a pair of vane pumps operating as the power unit and the motor unit thereof, means for conducting position the outer ends of the vanes in engagement with their respective cylinder walls before fluid is conducted to the motor unit for actuation thereof, said last mentioned means comprising a valve positioned in the flow passage between the power unit and the motor unit, and means for actuating said valve in response to the pressure in the discharge side of said power unit.

'7. A hydraulic transmissioncomprising a pair of substantially identical unit structures each of which consists of a main housing unit having an open end, a casing for a vane type power unit disposed within said housing and integral therewith, a reservoir chamber within said housing formed between the walls of said housing and said casing and having an open end wall, a vane type power unit mounted within said casing, a power shaft for said power unit extending through a common wall for said casing and said housing and journalled therein, a partition wall plate forming an end closure wall for both of said housings to separate the same into indefluid pressure from the dischargeside or the power unit to the under side of the vanes of both of said units for maintaining the outer ends of the vanes in engagement with their respective cylinder walls, and means for establishing positive pressure in the discharge side of said power unit to position the outer ends of the vanes in engagement with their respective cylinder walls before fluid is conducted to the motor unit for actuation thereof, said last mentioned means establishing circuit flow from the power unit to the motor unit upon establishment of a predeterainted pressure on the discharge side of the power 8. A hydraulic transmission having a pair of vane pumps operating as the power unit and the motor-unit thereof, means for conducting fluid pressurefromthedischargesideoithepower unittotheundersideofthevanes ofbothot said units for maintaining the outer ends of the vanes in engagement with their respective cylinder walls. means for establishing positive pressure in the discharge side of said power unit to pendent power units, a flow passage in said casing connecting said reservoir to said vane type power unit, a second flow passage in said casing from said vane type powerunit to the exterior of said casing and, terminating in the same plane as said open end wall, said unit structures being mounted upon opposite faces of said partition with said second passages and said chamber openings adjacent opposite faces of said partition, passages in said part tion interconnecting the reservoir chambers in said housings and said second flow passages, whereby fluid circuit flow is established for the hydraulic transmission and one of said'units acts as a power unit while the other acts as a motor unit, means for conducting fluid pressure from .power unit to the under side of the vanes of both of said units to place the same in operative positionin each of the units. valve means in said second now passage {or controlling fluid flow therethrough, and pressure actuated means responsive todischargepressure ofsaidunit'acting as a power unit for operatingsaidvalvcmcanswherebytocauseapositivefluidprcsmrctobcbuiltup insaidpowerunitfordellvery'totheundcrsidc oithsvsnesbeforeintereonnsctinstbessmefor the discharge side of said 

